MRI has recently emerged as an important modality for imaging global and regional function of the heart, because of its good image quality and its unique ability to quantify regional motion. Quantification makes MRI observer-independent and objective. In addition, MRI quantification can reveal transmural regional function. MRI, however, suffers from several limitations that make it clinically limited for quantifying regional function, despite its image quality and unique abilities. These limitations include the need for long imaging times, which often requires breath holding, and long and difficult post-processing for motion quantification. On the other hand, an imaging technique that reveals regional function directly, i.e., does not require post-processing, would not only eliminate analysis time, but also would shorten imaging time. We propose a technique for encoding the regional function directly from MR images that will enable continuous imaging of regional function without the need for breath holding. We have recently reported that strain encoded (SENC) MRI produces images whose regional brightness depends on the regional function of the heart, which can be viewed as a non-physical contrast, called strain contrast. In preliminary SENC experiments with patients and dogs, dysfunctional regions in the heart appeared hypo-enhanced (or hyper-enhanced) relative to remote normal regions. In this research, we will develop and validate a SENC MRI system for continuous (i.e., no need for breath holding) online imaging of regional function of the whole heart. The system will run continuously during a dobutamine stress test, providing real-time monitoring of changes in regional function, and automatically detect ischemic changes.
Our specific aims are to 1) improve the quality of SENC images and the sensitivity of the strain contrast, and test the hypotheses that 2) continuous imaging of regional function using fast SENC has the same accuracy in quantifying regional function as 3D MR tagging, and 3) that the SENC MRI system can automatically detect changes in regional function in the whole heart. By the end of this project, we will have developed and validated the SENC MRI method for continuous monitoring of regional function and will then be ready to perform clinical studies on a larger number of patients. Our long-term goal will be to compare the clinical sensitivity and specificity of SENC for determining viability against other existing modalities, such as SPECT, PET, or dobutamine stress echo.
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